I really question all those people who say the DC Metro is great.

If you're taking the train solely to/from downtown DC during the morning and evening rush hours, it's generally more or less reliable (although crowded.)

However, if you're taking the train at off-peak hours - particularly on weekends - the system becomes a Dantesque hellscape. It's not unusual to find numerous stations shut down for construction, or for trains to use one set of tracks for both directions, adding 30+ minutes to what should be a 15-minute trip.

If you're based in downtown DC, most of the main tourist attractions can be reached easily on foot or by bus, so that shouldn't be too much of a problem. However, if you stay out in a suburban hotel (which are often *much* cheaper than those in the District proper) and expect to commute in on Metro over a weekend, you could find yourself stuck with long waits.

Also, with regard to safety in DC - as a tourist you're unlikely to run into any problems. However, crime is certainly not uncommon even in so-called "nice" areas and downtown, particularly at night. And keep in mind that some of the city's main nightlife areas - such as U Street, Columbia Heights, and H Street NE - were until recently 100% the ghetto, still have lots of public housing, and do with some frequency see muggings, street attacks, and shootings (the latter usually between/among criminals, but still.)

Don't let the fact that you see giant luxury condo buildings and restaurants/bars all around lull you into a false sense of security in DC. I'd say the crime risk is more akin to that in Mexico City (the nicer parts) than in NYC or Chicago or other big US cities where tourists go. Again, you're extremely unlikely to have a problem, but at least recognize that the risks are higher than you might expect them to be, and maintain the appropriate level of vigilance.